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1.
An improved version of Doyle integral method for the determination of the kinetic parameters from nonisothermal thermoanalytical data has been presented. The relative errors involved in the activation energy and frequency factor determined from Doyle integral method and its improved integral method have been estimated. The results have shown that the precision of the improved version of Doyle integral method for the determination the kinetic parameters (including the activation energy and frequency factor) is much higher than that of Doyle integral method.  相似文献   

2.
The kinetic analysis of the degradation of polystyrene (PS) in supercritical acetone has been studied using the nonisothermal weight loss technique with heating rates of 3, 5 and 7 °C/min. The weight loss data according to degradation temperature have been analyzed using the integral method based on Arrhenius form to obtain the kinetic parameters such as apparent activation energy and overall reaction order. The kinetic parameters obtained from this work were also compared with those of the thermal degradation of PS in nitrogen atmosphere. From this work, it was found that the activation energies of PS degradation in supercritical acetone were 73.3-200.7 kJ/mol and lower than those of the thermal degradation in nitrogen atmosphere.  相似文献   

3.
Methods for the calculation of activation energies, pre-exponential factors and reaction orders from thermogravimetric data are briefly reviewed. A new integral method is proposed for the determination of these kinetic parameters, using data from pairs of TG curves produced at different heating rates. Employing accurate values of the temperature integral of the Arrhenius equation, tabulated over a range ofE andT, and a simple graphical procedure, the method offers advantages of speed and accuracy over those previously reported. It is suggested that at least one of the kinetic parameters should be allowed to move freely in order to achieve the best possible fit between calculated and experimental traces.  相似文献   

4.
A new integral method of nonisothermal kinetic analysis has been developed with the dependence of the frequency factor on the temperature (A = A 0 T m ). The new integral method is obtained from the newly proposed approximation for the general temperature integral, which is more accurate than the other existed approximations. For applications, nonisothermal thermoanalytical data obtained by theoretical simulation have been processed. The results have shown that the newly proposed integral method is an ideal solution for the evaluation of kinetic parameters from nonisothermal thermoanalytical data with the frequency factor dependent the temperature.  相似文献   

5.
利用模式搜索法求取了一个新的温度积分近似式,给出了相应的估算动力学参数的方程。新的温度积分近似式根据数值计算结果得到,可靠性高。讨论了新的近似式计算值与温度积分数值积分结果的偏差。与其它近似式相比,新的温度积分近似式的表达式简单,精确度更高,非常适合非等温过程的动力学参数的计算。  相似文献   

6.
The kinetic parameters have been calculated by the differential method according to Freeman and Caroll, the modified differential method, and the integral method according to Coats and Redfern. The calculations have been performed on the base of thermogravimetric data obtained on the recording vacuum thermoanalyzer TA 1 (Mettler). The automatic processing of measured values for off-line operation was carried out by means of data transfer (Mettler) using the small computer KRS 4200. Information on the system and the accuracy of data transfer is given.The methods have been compared for the dehydration of calcium oxalate, the formation of metakaolinite, the oxidation of petroleum coke, and the dehydration of montmorillonite. Using the differential method, in part, kinetic parameters have been obtained which cannot be interpreted in a physical sense. In order to determine the causes of different results, the effects of various mathematical procedures have been studied. This study and the comparison with literature data indicate that the programme for the determination of kinetic parameters by the integral method as described gives the most reliable results.  相似文献   

7.
Thermal decomposition kinetics and mechanism of layered double hydroxides (LDHs) intercalating different amounts and types of borate ions were studied using Coats–Redfern integral and Achar differential methods. The results revealed that the Coats–Redfern integral method is more appropriate than the Achar differential method for evaluation of the nonisothermal thermogravimetric decomposition data. The first-order Avrami-Erofe’ev A1 mechanism was found to be the best fitting kinetic model for almost all samples. In addition to the amount and type of the intercalated borate ion, interlayer orientation was also of importance in determining the chemical and thermal stabilities and hence the decomposition kinetics of the studied compounds.  相似文献   

8.
This study presents results on the kinetics of kaolinite dehydroxylation. The accuracy of various methods of determining the values for the kinetic parameters and their sensitivity in detecting the mechanism of reaction is investigated. In particular, the differential order of reaction method of Baker, the general method of Achar et al., the integral method of Boy and Bohme, and the method of Coats and Redfern as modified by Fong and Chen are considered.

Kaolinites from well-known sources are used to study the influence of crystallinity on the values of kinetic parameters. The statistical significance of the various mathematical methods for the assessment of the data obtained from non-isothermal thermogravimetry is determined by comparison with experimental and theoretical data using a computer programme developed for this purpose. The study demonstrates that the kinetic parameters can be used to quantify the degree of crystallinity of kaolinite and also confirms other findings that the dehydroxylation of kaolinite is a second-order reaction.  相似文献   


9.
An investigation of the curing (polymerisation) rate of acrylamide was carried out using isothermal and non-isothermal DSC in order to estimate the time for complete conversion of monomer at ambient temperatures. The non-isothermal data were used to model the rate using integral isoconversional and incremental isoconversional kinetic methods. Applying the equations for integral isoconversional methods and extrapolating to ambient temperatures resulted in non-sensical conversion–time curves, where the time estimated decreased for increasing degree of conversion to be reached. This odd behaviour was attributed to the incorrectness of the integration where the kinetic parameters (e.g. the activation energy) are a function of conversion. The problem was addressed by applying incremental methods which provided more reasonable results as the integration is carried out over small conversion increments where the kinetic parameters are assumed to be constant. Estimates of the conversion were compared to isothermal measurements and, although isothermal DSC produced significant variability in the data, extrapolated estimates from non-isothermal kinetic analysis produced, at best, an upper boundary for the estimation of the time to reach a fixed degree of conversion.  相似文献   

10.
The thermal polymerization kinetics of dimethacrylate monomers was studied by differential calorimetry using non-isothermal experiments. The kinetic analysis compared the following procedures: isoconversional method (model-free method), reduced master curves, the isokinetic relationship (IKR), the invariant kinetic parameters (IKP) method, the Coats-Redfern method and composite integral method I. Although the study focused on the integral methods, we compared them to differential methods. We saw that even relatively complex processes (in which the variations in the kinetic parameters were only slight) can be described reasonably well using a single kinetic model, so long as the mean value of the activation energy is known (E). It is also shown the usefulness of isoconversional kinetic methods, which provide with reliable kinetic information suitable for adequately choosing the kinetic model which best describes the curing process. For the system studied, we obtained the following kinetic triplet: f(α)=α0.6(1−α)2.4, E=120.9 kJ mol−1 and lnA=38.28 min−1.  相似文献   

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